Kelthaz, how, exactly, is it unrealistic for an addiction to the power afforded by magic to evolve into a literal addiction to magic as a recreational drug?
How is it unrealistic for an addiction to magic
to be similar to an addiction to drugs? Well, you've got me there. What was I thinking.
Or, in the context of the show, magic is not drugs. It's power. Giles even clearly states that in the first episode of Season 7. They were trying so hard to shoehorn in a real life issue that they very awkwardly turned Willow's magic issues into a very special episode about drugs. Her going to that drug dealer to shoot up with magic completely killed any interest I had in that arc that started in season 2.
Actually, Giles in no way, shape, or form says that magic is not drugs. The only thing that Giles says is that, for Willow, it's no longer about dabbling in magic as a hobby or literally using magic to get high; the magic is literally inside her now (seeped into her very being) and it's about learning control.
Season 6 isn't the first time in the series that there were hints that magic could be used to produce drug-like euphoria; it first happened way back in Season 2 with The Dark Age, when Giles makes it pretty clear that he and his friends were using magic to 'get high'; it wasn't quite as literal a situation as presented in Season 6 given that what they were really doing was using the influence of the demon to get high rather than the magic itself, but the underlying principle was the same.
The detractors of Season 6 act like the whole 'magic = drugs' thing came completely out of nowhere and was a complete subversion of where things were headed vis a vis Willow's story arc, but it really isn't; it is certainly a new twist to the story, but it's not an unprecedented one.